(a) Field of the Invention
The present invention is directed to the field of particle sorting in micro-fluidic devices.
(b) Description of Related Art
The simple and continuous micro-fluidic fractionation of the different components of a blood sample with high selectivity is a challenge. More generally speaking, the separation of the different constituents of a complex sample has been a subject of interest to the micro-fluidics community since the inception of the field, and a myriad of devices have been developed to accomplish this task. Some existing devices rely on external fields to exert a selective force on the different constituents of a sample. However, external components hinder the portability of the device, impose challenges such as high power consumption, and overall, increase their complexity. Other devices require a sieving matrix or some form of filtering, which makes them prone to clogging and limits their throughput.
In the separation of blood components, a common technique requires the chemical lysis of selective cells, which creates contamination and is particularly prone to introducing artifacts by altering the physiology of the enriched entities. The recirculation that ensues in these devices with confined geometries, in which the depth and width of the grooves is comparable to the height and width of the channel, has been used to effectively mix fluids at the micro-scale (Abraham D. Stroock et al., Chaotic Mixer for Microchannels, Science 295, 647 (2002)) (FIG. 1) and a lot of effort has been devoted to understand the properties of the helical flow above the grooves. Chen and Gao (Hsiu-Hung Chen and Dayong Gao, Particle enrichment employing grooved microfluidic channels, APL 92, 173502 (2008)]) used this recirculation to enrich particles by size in channels patterned with grooves, both channels and grooves having dimensions comparable to the dimensions of the particles (FIG. 2). However, less attention has been paid to the flow along the grooves.
Recently, Mao and Alexeev (Wenbin Mao and Alexander Alexeev, Hydrodynamic sorting of micro particles by size in ridged micro channels, POF 23, 051704 (2011)) carried out a computational study and showed that the flow along aligned slanted ridges patterned on the top and bottom surface of a straight channel can be used to deflect neutrally buoyant spherical particles to a different extent according to their size (FIG. 3). In their simulations, the separation between the ridges is larger than the radius of the particles, and inertial effects cause small particles to flow in the vicinity of the patterned surfaces and large particles to remain near the center of the channel. Thus, smaller particles are deflected by the flow along the grooves while larger particles are deflected in the opposite direction by the re-circulating flow.